When the architect Laura Clark told friends and family that she was planning to live in an underground former public lavatory in south-east London, responses ranged from hilarity to horror along with quite a few polite inquiries as to the state of her mental health. ‘I was known as Laura Toilets for a while,’ she says laughing. And there were moments during the project’s lengthy gestation when Clark questioned her own sanity. For a relatively small renovation, little more than 600sq ft, the project faced more than its share of planning setbacks.

Clark first spotted the loos – with their chained gates and boarded-up stairwells – in 2005, when she moved to London, having completed her degree at the Glasgow School of Art. It was exactly the sort of challenge that the young architect was looking for. ‘I’ve always loved the idea of micro-regeneration,’ she explains. ‘For me that’s about saving sites with an interesting history, but which have been abandoned and forgotten.’ Her initial plan was to transform the two adjacent ex-lavatories (men’s and women’s) into a bar or tiny cinema. ‘I pictured it as something quirky and fun that would breathe life back into a neglected part of the local landscape,’ she says.

However, bringing this particular site back to life was very nearly a lost cause. The loos were built at the point where three council boundaries met, and it took the best part of two years for Lambeth to establish that it was the council responsible for them. And then, this hurdle cleared, the bleak state of the economy at the end of 2008 meant that developing it into a commercial premises was no longer viable. Just as she was about to draw a line under her scheme, Clark realised she could rework her designs into a sleek one-bedroom apartment. Up until this point Lambeth Council’s regeneration department had been very positive about her proposals, but as soon as Clark revealed that she wanted to live in the loos, concerns were raised about pretty much every aspect of the build, from lack of light to lack of a view. It took many months, during which light levels were monitored and measured daily, to convince planners that the space was habitable.

Lambeth then discovered that the building wasn’t listed on the land registry. Suddenly the sale was in doubt: despite being responsible for them, Lambeth wasn’t sure if it owned the loos and therefore if it had the right to sell them. By this point Clark had spent more than £3,000 on solicitors and been through ‘endless meetings and beautiful drawings’ – but Lambeth had to put the building out to tender and advertise their existence for six months to see if anyone else would claim ownership.

Finally, it could sell. Clark had initially put in an offer of £20,000 for the freehold, but as the property included the pavement above, the council would offer only a leasehold agreement. This also knocked a significant amount off her offer.

In the middle of 2011 Clark found herself the proud owner of the underground public conveniences, built in 1929, last used some time in the 1980s and now filled thigh-high with rubbish. She lost no time in getting stuck in, working alongside builders and labourers in order to transform the dank and frankly creepy space into a bright and airy home. ‘I ended up doing a lot of the labouring work myself, because it was such horrid, hard work that I struggled to keep people on the job,’ she says. ‘And filling skips is character-building.’ For Clark, who fights mixed martial arts at semi-professional level, it was also good strength training. She even persuaded one of her sparring partners to help out with a sledge-hammer on the grounds that it would be good for their game. Remarkably, the entire project cost only £65,000. ‘But in fairness, I did have many years to work it all out,’ she says.

Today it is hard to imagine that the light-filled one-bedroom flat, with its streamlined shelves, glamorous gold-leaf bathroom and subterranean garden, was once a derelict public convenience. There are clues though. The tiles that form the splashback in the kitchen were reclaimed from the site’s original use, as was a mirror in the living-room. And propped on a kitchen shelf is a small public health poster warning of the perils of VD. But still, for Clark, this is home.